0.56 V , –20 dBm RF-Powered, Multi-Node Wireless Body Area Network System-on-a-Chip With Harvesting-Efficiency Tracking Loop Lingli Xia, Jiao Cheng, Neil E. Glover, and

Abstract

A battery-less, multi-node wireless body area network (WBAN) system-on-a-chip (SoC) is demonstrated. An ef ficiency tracking loop is proposed that adjusts the recti fier’s threshold voltage to maximize the wireless harvesting operation, resulting in a minimum RF sensitivity better than –20 dBm at 904.5 MHz. Each SoC node is injection-locke da n dt i m e - s y n c h r o n i z e dw i t ht h e broadcasted RF basestation power (up to a sensitivity of –33 dBm) using an injection-locked frequency divider (ILFD). Hence, every sensor node is phase-locked with the basestation and all nodes can wirelessly transmit TDMA sensor data concurrently. Designed in a 65 nm-CMOS process, the fabricated sensor SoC contains the energy harvesting recti fier and bandgap, duty-cycled ADC, digital logic, as well as the multi-node wir eless clock synchronization and MICS-band transmitter. For a broadcasted basestation power of 20 dBm (30 dBm), experimental measurements verify correct powering, sensor reading, and wireless data transfer for a distance of 3 m (9 m). The entire biomedical system application is veri fied by reception of room and abdomin al temperature monitoring.